The present invention relates to an air-conditioning system of a motor vehicle and to a method for operating the air-conditioning system.
DE 198 55 309 discloses an auxiliary heating device, in which an air-conditioning system is not only used for cooling, but also for heating. Thus, for example in the heating mode, the refrigerant of the air-conditioning circuit is routed along a branched-off line, bypassing the condenser. The evaporator then serves, in this heating mode, as a heat 10 emitting heat exchanger which transmits the heat generated in the compressor to the air to be heated. In the normal cooling mode, the evaporator serves for cooling the air, usually taking it below the dew-point temperature, so that the moisture present in the air condenses out on the evaporator. When there is a changeover to the heating mode, this condensation water will evaporate and enter the vehicle interior, with the result that, in particular, windshield fogging may occur. This is referred to by what is known as xe2x80x9cflash foggingxe2x80x9d. One provision to avoid this windshield fogging, according to DE 198 55 309, is for different heat exchanger surfaces to be provided for cooling and for heating. These different heat exchanger surfaces may be assigned to different heat exchangers, so that an evaporator may be provided for the cooling mode and an additional heat exchanger for the additional heating mode.
Such an air-conditioning system, in which an additional heat exchanger serving for heating the air is provided in the refrigerant circuit, is also known from DE 39 07 201.
The disadvantage of these known air-conditioning systems is that an additional heat exchanger has to be provided, in addition to the unchanged evaporator which serves exclusively for cooling the air. The additional heat exchanger requires additional construction space within the air-conditioning system. Since the construction space in present-day vehicles becomes ever more limited, an additional heat exchanger of this type has not yet found commercial application. Driving situations in which the additional heating heat exchanger will be required seldom occur, as a proportion of the total operating period of the motor vehicle. To be precise, these conditions occur mainly only during cold starting in the cold season, so that the additional gain in comfort and safety due to the additional heat exchanger cannot compensate for the disadvantages in terms of lost construction space and higher costs.
One object of the present invention is to provide an improved air-conditioning system.
A particular object resides in providing an air-conditioning system, by means of which the disadvantages mentioned can be avoided and by means of Which, in particular, the additional heat exchanger can be better utilized.
A further object of the invention is to provide an improved method for operating an air-conditioning system.
In accomplishing these objects, there has been provided in accordance with one aspect of the present invention an air-conditioning system for a motor vehicle, comprising: a refrigerant source including a compressor for providing compressed refrigerant and a first condenser; a housing for routing air that is to be conditioned; a first heat exchanger through which the air to be conditioned is capable of being selectively directed, positioned in the housing; a first evaporator positioned in the housing upstream of the first heat exchanger, the first evaporator being connected to the refrigerant source; a second heat exchanger positioned upstream of the first heat exchanger, the second heat exchanger being capable of being selectively connected to the refrigerant source; and a control circuit for the air-conditioning system, the control circuit being capable of switching between (1) a cooling mode in which the first evaporator and optionally the second heat exchanger are provided with condensed refrigerant from the refrigerant source, whereby the second heat exchanger optionally functions as an evaporator, and (2) a heating mode in which the second heat exchanger is selectively provided with compressed refrigerant from the refrigerant source and functions as a condenser.
In accordance with another aspect of the invention, there has been provided a method for operating an air-conditioning system as described above, comprising: operating the system in the cooling mode, wherein refrigerant is supplied to the second heat exchanger; switching the system to the heating mode; and after permitting lapse of a predetermined minimum period of time, supplying the second heat exchanger with compressed refrigerant.
Further objects, features and advantages of the invention will become apparent from the detailed description of preferred embodiments that follows, when considered together with the accompanying figures of drawing.